The present invention relates to an operating mode switching apparatus for a hammer drill which comprises a percussion mechanism as well as a rotational force transmitting mechanism.
For example, a conventional hammer drill is equipped with a motor. The motor causes a rotational force for driving a tool attached on a front end of the hammer drill. The rotational force of the motor is transmitted to an intermediate shaft via a first pinion and a first gear. A second pinion is provided on the intermediate shaft. The second pinion meshes with a second gear. Thus, the rotational force of the motor is always transmitted to the second gear. The second gear meshes with a rotary cylinder. A rotational force of the second gear is thus transmitted to the tool attached on the front end of the hammer drill via the rotary cylinder.
The intermediate shaft is a castellated portion for spline engagement with a sleeve. This sleeve is selectively engageable with a motion converting member. The motion converting member is coupled around and rotatable about the intermediate shaft. When the sleeve is engaged with the motion converting member, the rotational force of the motor is transmitted from the intermediate shaft to a piston via the motion converting member. The piston, acting like an air spring, reciprocates to cause a compression force which is transmitted as a percussion force to the tool via a percussion element and an appropriate intermediate element.
The operating mode of the hammer drill is changeable by manipulating a mode switching member which is, for example, rotatably provided on an outer casing of the hammer drill. The rotational motion of the mode switching member is linked with the sliding motion of the sleeve. When the mode switching member is rotated by an operator, the sleeve shifts in the axial S direction to change the engaging condition between the sleeve and the motion converting member. Thus, the operating mode of the hammer drill is changeable depending on the preference of the operator. For example, both of the rotational force and the percussion force can be transmitted to the tool in one mode. Only the rotational mode can be transmitted to the tool in another mode by manipulating the switching member.
Unexamined Japanese Patent Application No. 3-504697, corresponding to PCT/DE89/00336 (WO89/11955), published in 1991, discloses a hammer drill having three modes of "rotation+percussion", "rotation only" and "percussion only" which are arbitrarily selectable depending on user's preference.